Public mobile communication system compatible wireless communication system

ABSTRACT

The equipment has a wire interface for connection to a wire-Line telecommunication network and an air interface to communicate with mobile stations in accordance with a cellular network operating mode. Each mobile station operates in conjunction with a plug-in subscriber identity module containing parameters used to set up and/or manage the calls. The equipment also has a data reader/recorder suitable for receiving a subscriber module, reading certain parameters from it and writing to it other parameters dependent on the equipment. Telephone calls using a mobile station in conjunction with a subscriber identity module previously inserted in the reader/recorder may then be set up via the wire-line network.

BACKGROUND OF THE INVENTION

The present invention relates to a telephone equipment of the cellularradiotelephone base station type.

The operator of a mobile telephone network distributes the base stationsof the network across the territory to be covered, whereby the areascovered by the base stations define the cells. These base stations arelinked to other mobile service infrastructures designed to route callsand link up with the wire-line networks.

Certain subscribers to the cellular network may have a wirelesstelephone station in their home or generally in a private place, similarto a private base station, directly connected to a wire-linetelecommunication network. When the mobile station is communicating fromthe subscriber's home, it accesses this private base station inpreference to those of the cellular network. The call is thereforerouted via the wire-line network and not via the cellular network. As aresult of these arrangements, the subscriber can substitute his mobilehandset for the wire-line terminal conventionally used at home.

An object of the present invention is to facilitate the use andinstallation of such private base stations.

SUMMARY OF THE INVENTION

Accordingly, the invention proposes a telephone equipment comprising awire interface for connection to a wire-line telecommunication networkand an air interface for communicating by radio with mobile stations inaccordance with an operating mode of one type of cellular network, eachmobile station operating in conjunction with a plug-in subscriberidentity module containing parameters specific to the subscriber holdingthe mobile station and used to set up and/or operate radio calls. Theequipment further comprises a data reader/recorder capable of receivinga subscriber identity module, reading therefrom at least one of theparameters specific to the subscriber and writing thereto otherparameters dependent on the equipment, whereby telephone calls involvinga mobile station located within range of the equipment and associatedwith an identity module that was previously inserted in the datareader/recorder can be set up via the wire-line network by means of thewire interface and the air interface.

The data reader/recorder enables the exchange, between the subscriberidentity module and the private base station telephone equipment, of theparameters needed for the interaction of the base station and the mobilestations, i.e. on the one hand the parameters which allow the mobilestation to identify the equipment as it is detected by radio and thentake the required steps with the cellular network and, on the otherhand, the parameters which enable the equipment to route incoming callsto the mobile station.

Use of this private station is not reserved for a single subscriber. Asubscriber other than the one holding this equipment may register withthis equipment by presenting his subscriber identity module to it. It isalso conceivable for several subscriber modules to be registeredsimultaneously in order to be able to communicate via the equipment.

Another advantage is that the equipment may be issued to the userindependently of the mobile station, which he may have acquiredpreviously, in which case the reader/recorder merely has to read andre-programme the subscriber module presented to it.

Another aspect of the present invention relates to a telephone equipmentof the private base station type comprising a wire interface forconnection to a wire-line telecommunication network and an air interfacefor communicating by radio with mobile stations in accordance with anoperating mode of one type of cellular network, wherein telephonecommunications involving a mobile station located within radio range ofthe equipment may be set up via the wire-line network using the wireinterface and the air interface, and wherein the air interface isarranged to transmit a beacon signal in accordance with the operatingmode of the type of cellular network, so that it can be detected by amobile station located within radio range of the equipment and to ceasetransmitting the beacon signal during a call set up via the wire-linenetwork and involving a mobile station. This equipment preferablyincorporates the data reader/recorder defined above.

This equipment has the advantage of limiting the radio interferencewhich it causes in the cellular network and/or other equipment of thesame type. One simple solution is to arrange the air interface so thatit occupies the physical channel of the beacon signal during said callinvolving the mobile station.

However, if several mobile stations are likely to communicate via theprivate base station (for example because their subscriber modules weresuccessively submitted to the reader/recorder), the fact that one ofthem is making a call will cause the beacon signal to be interrupted andthe equipment will no longer be detected by the other mobile station orstations. They will then locate on the cellular network so that theywill still be capable of transmitting or receiving calls in spite of thefact that the line to which the equipment is connected is engaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an equipment as proposed by the invention;

FIG. 2 is a flow chart illustrating a procedure by which the equipmentis configured.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a telephone equipment 4 consisting of a private basestation for a subscriber to a cellular telephone network. This stationis installed in the home of the subscriber or more generally in an areain which he wishes to obtain private radio coverage.

The equipment 4 has a wire interface 5 to be connected to a wire-linetelecommunication network 6, such as an analogue switched telephonenetwork, for example. The interface 5 operates in a conventional mannerusing the protocols of the wire-line network 6.

The equipment 4 also has an air interface 8 connected to thetransmitting/receiving antenna 9. The radio range of the equipment istypically that of a conventional cordless telephone (less than 300meters).

In the specific example described here by way of illustration, the airinterface 8 operates in accordance with the European GSM radiotelephonesystem used in numerous cellular networks.

In particular, the interface 8 forms a broadcast common channel (BCCH)at a certain beacon transmission frequency. This frequency may beassigned to the equipment by the local network operator or it may bedetermined by the equipment automatically from a band of frequenciesallocated to the network. In order to do this, the interface 8 maylisten in to the frequencies in the allocated band and select the one onwhich the detected power is the lowest, so as to minimise interference.

The private base station 4 transmits a beacon signal on the BCCHchannel, which provides, in particular, a cellular networkidentification code. This code usually enables the mobile stations todistinguish between different networks of the same type (GSM in ourcase) which may co-exist in certain areas. In our application, thiscode, referred to as PLMNC, identifies a private network made up of asingle cell corresponding to the coverage provided by the equipment 4.

The mobile stations operating with the equipment 4 are adapted to accessthis private network in preference to other networks of the same type.

Such adaptation can be simply made through an automatic networkselection mechanism such as that described in the standard GSM 03.22:<European digital cellular telecommunications system (Phase 2);Functions related to Mobile Station (MS) in idle mode>, EuropeanTelecommunications Standards Institute, Sophia Antipolis, France,November 1994, ETS 300 535. When a mobile station previously registeredwith the equipment 4 is switched on, this station looks for the privatenetwork corresponding to this equipment If this private network cannotbe found (i.e. the mobile station is out of range of the equipment 4),the mobile station then tries to access its home cellular network (homePLMN) or another cellular network. If a mobile station is serviced byits home cellular network, it will check periodically to ascertainwhether it can detect the presence of the beacon signal of the equipment4. If this signal is detected, the mobile station attempts to access theprivate network. If this signal is lost, the mobile station issues alocation update request to its home cellular network.

GSM mobile stations operate in conjunction with a plug-in subscriberidentity module (SIM card) which carries all the data specific to thesubscription. In particular, this module stores the international mobilesubscriber identity (IMSI) as well as the associated individualauthentication key K_(i).

The equipment 4 illustrated in FIG. 1 has a conversion unit 10 betweenthe interfaces 5 and 8. This unit 10 performs the variousanalogue-to-digital or digital-to-analogue conversions, speechcoding/decoding and shaping of the signal frames required to make theinterfaces 5 and 8 communicate. A control unit 12 intercepts thesignalling messages received on the interfaces 5 and 8 and controlsthese interfaces 5, 8 and the conversion unit 10 as appropriate.

The control unit 12 is connected to a memory 13 as well as a userinterface comprising a keyboard 14 and a display screen 15, for example.It is also connected to a data reader/recorder 16 provided for receivinga SIM card 17.

The reader/recorder 16 is used to exchange certain parameters with theSIM card 17 as part of a subscriber registration procedure with theequipment 4. Certain parameters, in particular the mobile subscriberidentity IMSI, are read from the SIM card and stored in the memory 13,whilst other parameters, in particular the PLMNC network card assignedto the equipment 4, are written to an available memory zone of the SIMcard 17.

In order to assign certain parameters to the private base station 4, thereader/recorder 16 may be set up to receive another plug-in data medium,referred to as a customisation card or module, containing parametersthat will be indicated below. This customisation module has the sameformat as a SIM card. It has a storage zone, e.g. magnetic, but it isnot necessarily a chip card.

FIG. 2 illustrates one example of how the private base station 4 and aSIM card may be configured.

In an initial step, the control unit 12 determines whether the station 4needs to be configured (step 20). This is the case for example when thebase station 4 is switched on or in response to a configure commandentered by the user from the keyboard 14. In this case, the user isprompted to insert his customisation card in the reader/recorder 16, bya message issued on the display screen 15 (step 21). Once thiscustomisation card has been inserted in the reader 16, the control unit12 issues a command for the following parameters stored on this card tobe read and then written to the memory 13 (step 22):

network code PLMNC allocated to the private base station 4;

private authentication key K_(i) specifically assigned to theauthentication and encryption operations performed within the privatenetwork

an indication B of the frequency band used for the radio signals withinthe private network;

authorised transmission power P for the air interface air for mobilesignals within the private network, in particular for the beacon signal;

duty cycle ρ for transmission of the beacon signal on the BCCH channel;since the GSM system is of the time division multiple access (TDMA)type, each TDMA frame being sub-divided into N=8 successive timeslotswhich may be assigned to different transmissions/receptions, and sincethe private network does not have another cell to be monitored by themobile stations, the beacon signal may be transmitted during n timeslotsover N (1≦n≦N), which gives p=n/N

secret authorisation code NA for registering a subscriber identitymodule with the private base station 4.

These parameters carried by the customisation card are defined by theoperator of the subscriber's home network in accordance with thearchitecture and characteristics of this network.

Alternatively, rather than reading the values of these parameters from aplug-in customisation card, the control unit 12 could obtain them viathe interface 5 by running a downloading programme which would query aserver connected to the wire-line network 6 and controlled by theoperator of the cellular network, in which the parameters in questionwould be stored.

At step 23, the user is prompted to enter from the keyboard 14 thedirectory number of the line of the wire-line network 6 to which theequipment is connected. Once entered and validated, this number isrecorded in the memory 13 at step 24.

The holder of the private base station might also be able to choose thesecret authorisation code NA, which would then be entered from thekeyboard 14 rather than being read from a customisation card ordownloaded.

Once the station 4 is configured, the control unit 12 determines, atstep 25, whether a SIM card has been inserted in the reader 16 and needsto be registered with the private base station 4, for example if theuser has entered a command to register from the keyboard 14. The firststep 26 of this registration procedure consists in prompting the user toenter the registration authorisation code NA. If the user enters thecorrect code from the keyboard 14, the control unit 12 issues a commandto read the mobile subscriber identity IMSI in the memory of the card 17and write this identity to its memory 13 (step 27). At step 28, it thenissues a command to write the parameters PLMNC and K_(i) obtained atstep 22 as well as the directory number NS to a zone provided in thememory of the SIM card 17.

Several SIM cards may be registered with the base station 4 in thismanner.

Once this registration has been completed, the private base station 4switches to its nominal operating mode.

In particular, it takes account of the parameters B, P, ρ obtained atstep 22 of the configuration, transmitting the beacon signal at themaximum power P and the duty cycle ρ on a channel of the BCCH type,whose frequency is selected from the band B in the manner describedabove. The SIM card 17 is removed from the reader 16 and re-inserted inthat of the mobile station. When switched on, the latter willinitialise, giving priority to the private network.

If the private base station 4 detects an access request from a mobilestation (random access channel RACH), it establishes a signallingchannel and obtains from the mobile its identity IMSI. It then checksthat this IMSI is in fact registered in its memory 13. This check avoidsany problems of conflict between two neighbouring private base stationswhich would have the same network code PLMNC.

If the check is negative, the mobile station is denied access to theprivate network. Otherwise, the equipment 4 proceeds with authenticationof the mobile station in a manner similar to that specified in the GSMstandard but using the private key K_(i). It generates a random number Rwhich it communicates to the mobile station and computes another key Sas a function of R and K_(i) by applying a confidential algorithm. Themobile station receiving the number R proceeds with the same computationusing the key K_(i) which was stored in the SIM card at step 28 andreturns the computed result S to the station 4. If the key S computed bythe station 4 matches, access is authorised.

Once access has been authorised, the mobile station automaticallyactivates in its home location register (HLR) of the cellular network acall forwarding service to the directory number NS which was registeredin the SIM card. Accordingly, any call destined for the mobilesubscriber will be routed through the equipment 4 via its connectingline to the wire-line network 6. Alternatively, the call forwardingservice could be activated by the private base station 4 via thewire-line network 6 and an appropriate interface between the latter andthe HLR.

When setting up a call involving the mobile station (outgoing orincoming), the latter computes an encryption key using the secret keyK_(i), a random number and another confidential algorithm. The sameencryption key is computed by the station 4 and used to encrypt themobile communications. The call then proceeds as a call from thewire-line network via the interfaces 5 and 8 and the conversion unit 10,the mobile station being used in a similar manner to that of a cordlesstelephone.

If the mobile station loses the mobile link to the equipment 4, it willautomatically run a location update procedure with its home network.This mobile station or the base station 4 will also issue a command todeactivate the call forwarding service.

It may be noted that an automatic transfer (handover) between theprivate base station and a base station of the cellular network isimpossible. However, the system may be arranged so that the airinterface 8 supports an automatic intra-cellular transfer mechanism.

On the other hand, the air interface 8 may implement other mechanismsprovided in the cellular system, such as frequency hopping, for example.

In general, it is advantageous if the duty cycle p for transmission ofthe beacon signal is equal to 1/N, in order to limit interference withthe base stations of the cellular network and the other privatestations, this ratio p not necessarily being programmable. The BCCHchannel carrying the beacon signal will then occupy one timeslot out ofN=8 in the TDMA frames. This timeslot may be selected by the privatebase station, like the beacon frequency, by means of a listening-inprocedure in order to minimise interference with the radio environment.

During a call involving a mobile station through the wire-line network6, the unit 12 controls the air interface 8 in order to interrupt thetransmission of the beacon signal.

In particular, the interface 8 may allocate to the downlink radiotransmission the physical channel previously occupied by the beaconsignal, i.e. the TDMA timeslot allocated to the BCCH on the beaconfrequency.

Every other mobile station whose SIM card has been registered and whichis within range of the station 4 will then lose detection of the beaconsignal and will spontaneously locate with its home cellular network sothat it remains perfectly capable of communicating via the cellularnetwork even though the wire-line is engaged. Once the call isterminated, the beacon signal is re-established and this other station,if still within range of the equipment, will try to access the privatenetwork again.

What is claimed is:
 1. Telephone equipment comprising: a wire interfacefor connection to a wire-line telecommunication network; an airinterface for communicating by radio with mobile stations in accordancewith an operating mode of one type of cellular network, each mobilestation operating in conjunction with a plug-in subscriber identitymodule containing parameters specific to the subscriber holding themobile station and used to set up and/or operate radio calls; and a datareader/recorder capable of receiving a subscriber identity module,reading therefrom at least one of the parameters specific to thesubscriber and writing thereto other parameters dependent on theequipment, whereby telephone calls involving a mobile station locatedwithin range of the equipment and associated with an identity modulethat was previously inserted in the data reader/recorder can be set upvia the wire-line network by means of the wire interface and the airinterface.
 2. Equipment according to claim 1, wherein the parametersspecific to the subscriber read in the identity module inserted in thereader/recorder comprise a mobile subscriber identity.
 3. Equipmentaccording to claim 1, wherein the parameters dependent on the equipmentwritten to the identity module inserted in the reader/recorder comprisea key for authenticating the mobile station and/or encrypting radiocommunications.
 4. Equipment according to claim 1, wherein theparameters dependent on the equipment written to the identity moduleinserted in the reader/recorder comprise a network identity code, amobile station associated with said identification module being arrangedto access a private network consisting of the equipment, to which saidnetwork identity code is assigned, in preference to other cellularnetworks.
 5. Equipment according to claim 1, wherein the reader/recorderis further arranged to receive a customisation module and read therefromat least part of the parameters dependent on the equipment which arethen written to an identity module inserted in the reader/recorder. 6.Equipment according to claim 5, wherein the reader/recorder (16) isarranged to read additional parameters in the customisation module. 7.Equipment according to claim 6, wherein said additional parametersinclude a secret authorisation code for registering a subscriberidentity module, the dialling of which is requested subsequently inorder to authorise read and write operations in a memory of a subscriberidentity module inserted in the reader/recorder.
 8. Equipment accordingto claim 6, wherein said additional parameters include an indication ofan authorised frequency band for the air interface.
 9. Equipmentaccording to claim 6, wherein said additional parameters include anauthorised transmission power for the air interface.
 10. Equipmentaccording to claim 6, wherein said additional parameters include a dutycycle for transmission of a beacon signal by the air interface. 11.Equipment according to claim 1, further comprising downloading means forobtaining, from a server connected to the wire-line network, at leastpart of the parameters dependent on the equipment which are then writtento an identity module inserted in the reader/recorder.
 12. Equipmentaccording to claim 11, wherein the downloading means are arranged toobtain additional parameters from the server.
 13. Equipment according toclaim 12, wherein said additional parameters include a secretauthorisation code for registering a subscriber identity module, thedialling of which is requested subsequently in order to authorise readand write operations in a memory of a subscriber identity moduleinserted in the reader/recorder.
 14. Equipment according to claim 12,wherein said additional parameters include an indication of anauthorised frequency band for the air interface.
 15. Equipment accordingto claim 12, wherein said additional parameters include an authorisedtransmission power (P) for the air interface.
 16. Equipment according toclaim 12, wherein said additional parameters include a duty cycle fortransmission of a beacon signal by the air interface.
 17. Equipmentaccording to claim 1, wherein the air interface is arranged to transmita beacon signal in accordance with the operating mode of said type ofcellular network, so that it can be detected by a mobile station locatedwithin radio range of the equipment and to cease transmitting the beaconsignal during a call set up via the wire-line network and involving amobile station.
 18. Equipment according to claim 17, wherein the airinterface is arranged to occupy the physical channel of the beaconsignal during the call using said mobile station.
 19. Equipmentaccording to claim 17, wherein said type of cellular network uses timedivision multiple access, with signal frames each divided into severalsuccessive timeslots and wherein the air interface transmits the beaconsignal during one timeslot per frame on a beacon frequency and does nottransmit a signal during the other timeslots on the beacon frequency.